When the show opens we find that three siblings have been left on their own by their mother a few days after moving to a new place in London. With a nonworking stove and little food or money, they must work together to survive. This is not the first time they have been abandoned by their mentally unstable mother, but Maggie, 14 (Olivia Cygan), fears that this may be the time she does not return. She and her older brother, Eliot, 16 (Bryce Lunsky) have made a pact to conceal their situation from outsiders lest they be separated from each other and their 7-year old brother (a remarkably natural Gabriel Stern) and placed in foster homes.

Polly Stenham’s script hands us an interesting premise and plenty of places to go, but between establishing the scenario at the beginning and providing some revelations at the end, the unfocused script wanders from one repetitive argument to another without any engaging progression or character development. There are some nice moments, but the script flounders between them, filling the time with what seems like conflict for its own sake (no matter how dire the circumstance, nobody wants to hear two teenagers bicker perpetually). A new girlfriend (Austin Moore) is introduced, presumably to illustrate Eliot’s desire to be a normal teenage boy, but rather than adding an interesting new dimension to the plot, she remains a flat character whose departure makes as little impression as her entrance.

The dynamic between Maggie and Eliot is somewhat off-balance. The script calls for Maggie to be 14, but at a few years older, actress Olivia Cygancomes across as the older and more mature sibling; that the script has her behaving more responsibly than selfish Eliot only further muddies its suggestion that she is the dependent younger sister who has always looked up to her big brother. This is less of an issue when they are bantering , but when Eliot laments about having to be the responsible one, it’s hard to understand why he feels alone in carrying the mantle of parental burden. Maggie’s remark, “What brings you closer than sharing hell?” is a nice commentary on the survivor bond that develops between siblings who suffer together under abuse, but her accommodation of Eliot’s increasingly bizarre behavior would be easier to believe if she came across as younger and more naive.

Our credulity is further stretched in other ways. In one scene, the girlfriend yells at Eliot to let his siblings out of the basement where he has locked them “to get one minute of peace.” She yells this repeatedly while standing right in front of the basement door. Instead of turning and reaching out all of three feet to turn the latch, she throws her hands up and stalks out. In the final scene, the characters walk away from a clearly acceptable solution in a decision that makes no sense and is simply irritating.

The cast is fairly solid but misdirected. Overall, they do a good job of convincing us that they are siblings; the ease with which Maggie and Eliot interact, and their quasi-parental relationship with their younger brother is likewise very believable, but the repetitive shouting and shrill tones soon become grating, and the progressively heavy-handed performance as things fall apart devolves into melodrama. When their mother’s friends Katie and Roland (Joanne Underwood and Jeff McLane) arrive towards the end, you aren’t sure whether you are relieved because adults have entered to help the children, or because they might put a stop to all the whining.

There are good things about the show: the cast, the excellent English accents (kudos to dialect coach Kate Devore), Chad Bianchi’s visually engaging set (in which the walls are made of cardboard moving boxes to reflect the uncertainly and impermanence of the family), and Mac Vaughey’s rich lighting design. As it is, though, the show is exhausting and feels about 30 minutes too long. The script’s shortcomings could be mitigated by tightening the pace, finding the nuances, and reining in some of the performances. With the right treatment, the experience could be more satisfying.

Rating: ★★½

Tusk Tusk continues through October 7th at Noyes Cultural Arts Center, 927 Noyes, Evanston (map), with performances Fridays at 7:30pm, Saturdays at 2:30 and 7:30, Sundays at 2:30. Tickets are $25, and are available by phone (847-866-8049) or online through PrintTixUSA.com (check for half-price tickets at Goldstar.com). More info at PivenTheatre.org. (Running time: 1 hour 50 minutes, includes an intermission)